UPDATED. You’ll be surprised to learn how easy it is to understand how an airplane flies.
One of the most frequently asked questions I have received from my passengers after more than three decades as an airline pilot is “How does an airplane fly”? Well, here’s your answer:
What makes an airplane fly: The 4 basic principles of flight
Airplanes can fly because of four basic principles:
- Thrust moves you forward.
- Drag opposes thrust and works to counteract the thrust force.
- Lift keeps you flying in the air.
- Weight (Gravity) opposes lift and it wants to pull you to the ground.
The engines are used to create thrust, which is the motion that moves you forward.
Isaac Newton’s Third Law of Motion
Scientist Isaac Newton discovered that for every action (force in nature) there is an equal and opposite reaction. This is called Newton’s Third Law of Motion.
So, since thrust is a force that moves you forward there must be an opposite reaction working on slowing you down at the same time. Newton was right.
That opposing force of thrust is called drag.
What is airplane drag?
Drag is anything that creates friction on the airplane as it moves through the air. Air molecules and airplane skin friction, and the body of the airplane itself are just a few of the many things causing drag.
The engines move the airplane forward at high speed. The speed creates wind (called relative wind), that hits the front (leading edge) of the airplane wings.
(See the diagram above for illustration):
1) Air hitting the front of the wing:
When the wind molecules hit the front surface edge of the wing the air splits.
Some air goes over the top of the wing. The rest goes under the wing.
Next, something interesting happens. Because of the shape, or curvature of the wing:
2A) The air that flows on TOP of the wing:
The air flowing on top of the wing passes across the wing at a faster speed, but at a LOWER PRESSURE than the pressure existing below the wing. Air that moves fast creates low air pressure.
2B) The air that flows on the BOTTOM of the wing:
The air flowing below the wing passes across the wing at a slower speed, but at a HIGHER PRESSURE than the pressure created on top of the wing.
Because of this HIGHER pressure BELOW the wing, the plane can be kept up in the air. It’s like a “hand” holding up the wing.
3) Back of the wing
The back of the wing is called the trailing edge. The air coming from above and below the back of the wing surface accelerates down. That creates a downward force of air, further helping the wing stay in the air.
Airplane wing science and the Lift it produces
Bernoulli’s Principle and Aerodynamics
Long before airplanes were invented an Italian scientist, Daniel Bernoulli discovered his Bernoulli’s Principle.
He discovered that an increase in the speed of fluid (as it also applies to the air at the top of the curved wing) occurs at the same time that a decrease in pressure occurs. The decrease in pressure also coincides with a decrease in the fluid’s potential energy.
Thus the solution to how to make a wing fly was born.
The specialty field that deals with the mechanics of flight are called “aerodynamics“.
Weight (Gravity) explained
Do your recall Newton’s Third Law of Motion, telling us that for every action there is an equal but opposite reaction?
The force that works opposite of lift is called weight (gravity). Gravity is what keeps our feet firmly on the ground.
Gravity is defined as a force pulling two objects toward each other. Anything which has mass (earth) has a gravitational pull.
When you take off or climb lift must overcome (be greater than) weight. We achieve that with engine power by advancing the throttles.
At cruise, lift and weight are in a state of equilibrium.
During the descent to landing, weight must overcome (be greater than) lift.
Do you have any questions about this?
Of course, there is more to how an airplane flies than what you just read here.
But now you can consider yourself one of the few airline passengers with some knowledge of the subject when you board your next flight.
What do you think about this article, did it help you understand how an airplane flies? You can submit your comments or questions here.
Featured Image: Unsplash.